A wind turbine comprises a tower and a nacelle or machine housing supported on the tower and carrying the blades, rotor and electricity producing parts. A yaw system controls the position of the nacelle relative to the tower about a vertically extending yaw axis to thereby control orientation of the wind turbine rotor relative to the prevailing wind direction. If the wind turbine is not oriented correctly, the wind will impose uneven loads on the rotor and will seriously reduce the efficiency of the wind turbine. Therefore, the function of the yaw system is important in order to improve the efficiency and prolong the lifetime of the wind turbine.
The yaw system often comprises a toothed brake disc or ring fixed to the tower and a motor activated gear attached to the nacelle and meshing with the toothed gear so that activation of the motor results in a revolving of the nacelle thereby producing the yaw motion of the nacelle. The yaw drive or gear may also be separated from the brake disc. The yaw system may be provided with ball bearings or slide bearings for the yaw motion. The yaw system may also include one or more yaw brakes to maintain the nacelle and rotor in the correct yaw position.
The yaw brakes are typically engaged for extended periods of time in order to ensure that the nacelle is maintained in the correct position. The yaw brake typically comprises a brake calliper that in turn comprises at least one brake piston and a brake pad provided in a receiving part of the calliper. The brake disc is arranged in the receiving part of the brake calliper, and when the brake piston is engaged, the brake pad is compressed against the brake disc, thus providing a braking force due to a frictional engagement between the brake pad and the brake disc. The yaw brakes may also be partly engaged during yawing in order to control and dampen the yaw movement.
One of the problems that is encountered with yaw brakes is the large amount of effort required, when the installed yaw brakes need to be removed from the brake disc for service, such as replacing brake pads or replacing the entire yaw brake. The problems occur since the yaw brakes are typically arranged at quite a large distance from a working platform in the tower. Further, the brakes are currently handled by a service technician, which includes lifting of the yaw brake from the brake disc and down to the working platform or vice versa, which in turn is associated with health and safety risks. Additionally, current tools for assisting in lifting or lowering the yaw brakes are time-consuming to use, bulky and sometimes involve safety risks. The current tools are typically arranged on the floor of the working platform, thereby taking up floor space. Another problem with current service methods and tools is encountered due the inherent design of brake callipers, which entails that the brake calliper has to be moved horizontally before being lowered. The horizontal movement before lowering also involves safety risks in the current systems. The service or replacement of parts of the brake is normally done at floor level, whereas the servicing tools are located at waist height, which again involves health and safety risks.
Currently, when a brake needs a complete overhaul, the brakes are usually removed from the wind turbine entirely.